Industrial & Engineering Chemistry Research, Vol.40, No.20, 4363-4369, 2001
Using diffusion and electrical measurements to assess tortuosity of porous media
This study puts under scrutiny the unique relationship between molecular diffusion and electrical conductivity data for Berea, Okesa, Tallant, and Elgin sandstones ranging in permeability from 83 to 2502 md. The experimental setups used for generating the investigated data featured the use of a four-electrode circuit that canceled the effects of contact electrode polarization and a diffusion flow system that allowed on-line calibration and established a stable baseline. The effective molecular diffusion coefficients (De) for these porous media were estimated by matching simulated concentration profiles with measured ones. Tortuosity values were calculated by using molecular diffusivity models and their analogous electrical conductivity models. Tortuosity values calculated from diffusion measurements (using the Brakel and Heertjes model; Int. J. Heat Transfer 1974, 17, 1093) matched reasonably well with those values estimated using Pirson's electrical model (Geologic Well Log Analysis; Gulf Publishing: Houston, TX, 1983). These results indicate the superiority of the latter model over a large number of formation-factor-based models for estimating rock tortuosity. This study helped in the selection of adequate tortuosity models for characterizing sandstone rocks and verified the similarity between electrical conductivity and molecular diffusivity in sandstone rocks.